The invention relates to a release electromagnet assembly, and more particularly, to such assembly including a permanent magnet associated with a movable member and also including an electromagnet which cooperates with the magnet to produce a magnetic attraction therebetween which is effective to constrain the movable member and which is capable of producing a flux which opposes the flux from the permanent magnet, thus allowing the movable member to be released from constraint by the permanent magnet.
A release electromagnet assembly as may be used in an electrical shutter mechanism of a photographic camera includes a permanent magnet as is well recognized. Specifically, referring to FIG. 1, a conventional arrangement is shown which includes a permanent magnet 101 held sandwiched between yokes 102a, 102b of an integral U-shaped yoke assembly, and also includes a release coil 103 disposed on the magnet 101. Remote ends 102c, 102d of the yokes are effective to hold an armature piece 105 associated with a movable member 104 attracted thereto against the resilience of spring 106 which engages the movable member 104. The coil 103 may be energized to produce a magnetic flux which opposes the flux from the magnet 101, thereby allowing the movable member 104 to be released from constraint.
Such a release electromagnet assembly may be used in an electrical shutter mechanism of the camera, for example, for constraining a shutter closing member for a given period after a shutter opening member has been operated and before the shutter closing member is released by the energization of the electromagnet. A conventional electromagnet assembly of this kind requires the energization of the release coil with a current flow of such magntide which is sufficient to oppose the flux from the permanent magnet. Consequently, the magnetization of the magnet becomes gradually decreased until the attraction is eventually ineffective.
In consideration of such fact, the present applicant has proposed a release electromagnet assembly which again utilizes a permanent magnet for a constraining purpose without dissipating any electric power and which achieves the release by the use of an electromagnet separate from the permanent magnet to produce a flux which opposes the flux from the permanent magnet. The proposed assembly eliminates the initially mentioned disadvantage, and is also free from the aging effect, thus enabling a reliable operation. In addition, a reliable constraining and release operation is assured, thus providing an optimum arrangement for use in photographic cameras and electrical instruments of a reduced size.
Referring to FIG. 2A, an exemplary arrangement of the described release electromagnet assembly is shown in plan view. An electromagnet 1 comprises a channel-shaped yoke 2 which may be formed of a magnetizable material such as ferrite, and a release coil 3 disposed on the yoke 2. A permanent magnet body 4 which is adapted to be attracted by the solenoid comprises permanent magnet 5 having N- and S-poles at its ends adjacent to the ends 2a, 2b of the yoke, and an armature piece 6 formed of soft magnetic iron, permalloy or the like which is adhesively applied to the adjacent surface of the magnet. The body 4 is mounted on a movable member, not shown, by utilizing a hole 5a. The armature piece 6 is held attracted to the ends 2a, 2b of the yoke 2 as a result of the magnetization of the magnet 5, thus constraining the movable member in a given position. In order to release the movable member, the coil 3 may be energized, whereupon a flux is produced along a path a which opposes the flux from the magnet, thus allowing the armature piece 6 to be released and removed from the ends 2a, 2b. It will be seen that the movable member can be maintained in a given position without requiring any power, and the power is used only when it is desired to release the movable member. The purpose of the armature piece 6 applied to the magnet 5 is to provide a shunt path for the flux from the electromagnet, thus allowing the required repulsion to be produced with a reduced current flow, thereby improving operating efficiency.
FIGS. 2B, 3 and 4 show other examples of the release electromagnet assembly of the type mentioned above. In FIG. 2B, the body 4 comprises a pair of permanent magnets 5A, 5B which are separated by an interposed non-magnetic body 7. The magnets 5A, 5B have N- and S-poles, respectively, at their end abutting against the ends 2a, 2b, respectively, of the yoke 2. An armature piece 6 of a magnetically soft material is applied to the attracted side of the magnets while an iron piece 8 is applied against the other surface, thus providing a sandwiched structure. The provision of the iron piece 8 improves the efficiency of the electromagnet 1 by allowing a flux path a to pass through the iron piece.
The electromagnetic assembly of FIG. 3 is similar to that shown in FIG. 2A except that a mounting piece 9 is adhesively applied to the permanent magnet 5. The piece 9 is again formed of a magnetically soft material, and is applied to the opposite surface of the magnet from the armature piece 6. This achieves the similar effect as the electromagnet assembly shown in FIG. 2B.
In FIG. 4, a mounting piece 9 is integrally secured to an electromagnet 1 so as to be movable while a permanent magnet body 4 is stationary. In this instance, the attracted portions of the yoke 2 are located on the opposite or rear ends thereof, and are directly attracted to N- and S-poles of a permanent magnet 5. The body 4 includes an iron piece 10 in addition to the magnet 5, the piece 10 being adhesively applied to the opposite surface of the magnet from the attracting surface. A flux loop b is formed as shown.
In the arrangements described above in which the energization of the release coil 3 produces a flux which counteracts the magnetic attracting effect of permanent magnets 5, 5A, 5B, it is essential that the both ends 2a, 2b of channel-shaped yoke 2 be simultaneously removed from mating surface of the body 4. This involves a disadvantage that the attraction exerted by the permanent magnet cannot be eliminated unless the coil 3 is energized with an increased current flow. For this reason, in the prior art arrangement, the coil is connected with a capacitor having a high capacity which is in turn connected in shunt with a current supplying time constant circuit or power surface, in order to minimize the power dissipation of the source. Another difficulty of the described arrangements is manifest in the non-uniformity of movement of the magnet body as it is separated from the electromagnet. This results in the difficulty in adjusting the resilience of a coiled or torsion spring which is connected with the magnet body for separation thereof.